This invention relates to a method and apparatus for managing an access path between a host computer and a data storage system. More specifically, this invention relates to access path management in a multipath system where a data storage system is accessed via a plurality of access paths.
The storage capacity of data storage systems run by business organizations and the like is increasing from several reasons including a law that demands long-term storage of data coming into force and data taking a multimedia form. One measure to accommodate the increased storage capacity is to build a SAN (Storage Area Network), with which data sharing, high-speed access, and the like are made possible by connecting a plurality of host computers to disk arrays of a plurality of data storage systems through Fibre Channel or the like.
Placed between the host computers and the data storage systems are a plurality of equipments suitable for SAN connection, such as an HBA port, which is a port of a host computer bus adapter (HBA) connecting the host computers to the SAN, a CHA port, which is a port of a channel adapter (CHA) connecting the data storage systems to the SAN, a Fibre Channel switch, and a hub.
Connecting these equipments between the host computers and the data storage systems creates a plurality of physical paths.
The physical paths created between the host computers and the data storage systems bring path redundancy, which is effective against bandwidth shortage due to overload and such failures as one due to an out-of-order equipment.
The data storage systems each have a storage area composed of a plurality of physical disks. The storage area is partitioned into a plurality of logical volumes, and each of the logical volumes is provided to a specific host computer.
The host computer can choose from the plurality of physical paths laid between the host computer and the data storage systems a route to access the logical volume (hereinafter referred to as access path).
A SAN employs multipath management in which a plurality of access paths are set for one logical volume and the set plurality of access paths are managed.
Multipath management switches access paths when one of the equipments between the host computers and the data storage systems breaks down, thereby enabling the host computers to continue accessing the data storage systems. Multipath management can also balance the access load by using a plurality of access paths concurrently.
Companies that sell SAN-related equipments employ such a sales system for selling an equipment with a limited use of resources at a low price and then selling a right to lift the use limitations (hereinafter referred to as license) to a user who needs more resources of the equipment than initially allowed.
Users can lower the cost of running a SAN by using the minimum amount of equipment resources necessary for normal operation of the SAN and adding more resources as the need arises.
An example of this type of technology is found in JP 2005-165440 A, which discloses a technique of enabling a user to use only an actually necessary number of ports in a data storage system having a plurality of ports.